I have some version of Euphorbia inermis that I decided to plant in pure large pumice just as an experiment. To my shock, the plant immediately started to show signs of vigorous growth, within just 10 days. You can see this as light-shaded green tips in the photo below. That is unusual for this species, at least when I have grown them outdoors in other substrates. Can someone give me a hypothesis about why this might have happened growing in such large pumice particles? Additional oxygen is the only thing I can think of. I did NOT add any fertilizer to the water, and it was only watered ONCE.